(1) Field of the Invention
The present invention relates to marine tow cables and more particularly to marine tow cables that are used to measure the temperature of a water column.
(2) Description of the Prior Art
Knowledge of the temperature profile of the water column essential to optimize sonar performance. Currently, this information is often obtained through the use of expendable bathythermograph devices. For towed array applications, a continuous measurement could in principle be obtained with temperature sensors distributed along the length of the tow cable. If such a method could reduce the need for expendable bathythermograph devices, significant cost savings could result.
One system for measuring water temperature distribution without the need for such expendable bathythermograph devices is disclosed in U.S. Pat. No. 5,198,662 to Yamaguchi et al. In this system an optical fiber is suspended from a ship and towed by the ship to form an arc within the water. A measuring device for continuously monitoring temperature at various points along the length of the optical cable is provided. Sensors are also provided within the water depth at each of the various points along the length of the arc shaped optical fiber so that a temperature distribution at each water depth can be continuously measured. This patent does not, however, disclose a way for allowing temperature-sensing devices to be efficiently incorporated into the jacket of the cable.
It is known in the prior art that various organic polymers can be doped with electron acceptors and electron donors to achieve conductivity levels approaching those of some metals. Such polymers are known and are referred to herein as "conducting polymers".
Various uses have been suggested for such conducting polymers in electrical and optical fiber cables.
U.S. Pat. No. 5,313,185 to DeChurch, for example, discloses a continuous cable formed of a conducting polymer. The conducting polymer is extruded over a pair of elongated substantially parallel conductors that are spaced along the longitudinal length of the cable. This cable senses high temperatures when the conducting polymer filler melts and closes the circuit between the two conductors.
U.S. Pat. No. 5,382,909 to Massia et al. discloses the use of an electrically conducting polymer jacket for detecting liquid leaks. Two elongated conductors become electrically connected at a location that is determined by the leak, thus creating a system in which the connection point can be located by measuring the potential drop from one end of one of the conductors to the connection point.
While the cables described in the above mentioned DeChurch and Massia et al. patents make use of the electrical characteristics of conducting polymers, heretofore there has been no suggestion of exploiting the superior heat transfer characteristics of conducting polymers in optical fiber cable or electrical cable. A need, therefore, exists for an optical cable measuring water temperature distribution that makes use of the superior heat transfer characteristic of conducting polymers and allows heat sensors to be incorporated into the cable jacket.